Semiconductor structure having improved power handling and heat dissipation capabilities



p 1968 R. DAHLBERG ETAL 3,400,311

SEMICONDUCTOR STRUCTURE HAVING IMPROVED POWER HANDLING AND HEATDISSIPATION CAPABILITIES Original Filed' March 20, 1964 Fig. 2

J i ne'a'rffi ignhw Dieter ersmer WaHer Klossiko.

KITORNH [17b United States Patent 0 13 Claims. or: 317-235 ABSTRACT OFTHE DISCLDSURE A power transistor composed of a plurality of lowpowertransistor elements disposed in a common housing and each having anemitter resistor, all of the elements being connected together forparallel operation as a single transistor, and all of the elementspreferably being mounted on a common heat sink.

This is a continuation of application Ser. No. 353,491, filed on Mar.20, 1964, and now abandoned.

The present invention relates generally to the semiconductor art, and,more particularly, to a semiconductor arrangement which includes severalsemiconductor elements and especially transistors and/or diodes whichare connected together and disposed within a common housing.

In order to increase the power handling capability of such anarrangement, the active semiconductor surfaces can be enlarged. However,with an enlargement of the areas the yield goes down. Also, nosufiicient increase in power handling capability is obtained by thethermal couplings of the individual elements which results from simplyhousing several semiconductor elements in a common housing.

With these problems of the art in mind, it is a main object of thepresent invention to provide a semiconductor arrangement wherein severalsemiconductor elements are connected together and disposed within acommon housing and wherein their power handling capability is increased.

Another object of the invention is to provide a device of the characterdescribed wherein the entire electrical power loss is distributed amongthe individual elements as uniformly as possible.

Still a further object of the invention is to provide an arrangementwherein the maximum power handling capability in the form of heatdissipation is increased substantially.

These objects and others ancillary thereto are accomplished inaccordance with preferred embodiments of the present invention whereinthe uniform distribution of the electrical power loss or load isaccomplished in a surprising manner by the substantial electricaldecoupling of the individual elements from one another. A furtherimprovement is obtained by using semiconductor elements which aresubstantially identical with one another insofar as their electricalcharacteristics are concerned. If additional measures are taken toincrease the thermal coupling of the individual elements, then a maximumin power dissi pati-on is accomplished with an arrangement having thesmallest volume.

The electrical decoupling of the elements can be accomplished, forexample, by connecting resistors in the electrode leads. In usingtransistors, these resistors are preferably connected to the emitterlead. Capacitors may be connected in parallel with these resistors inorder to improve the high frequency characteristics. All in all, it hasbeen found that the better the thermal coupling of the individualelements, the less is the electric decoupling which is required, becauseof the relationship between electrical and thermal coupling.

The desired uniform distribution of the power loss or load on theindividual elements can be improved by using a common mounting plate forall of the elements because the individual elements are thermallycoupled with one am other by being mounted to the common base plate. Theelements are preferably soldered to the common plate. It is alsopossible to solder the elements to the common mounting plate by one oftheir electrodes. For example, with alloyed transistors, the collectoralloying pills of the elements are soldered to the common mounting placefor this purpose. The base of the common housing, for example, may beused as the common mounting plate.

In a further feature of the invention, the electrode leads are, at thesame time, constructed as electric fuses and the uniform distribution ofthe load is also maintained at the time an element fails to operate.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a vertical sectional diagrammatic view through oneembodiment of the present invention.

FIGURE 2 is a perspective diagrammatic view, partially broken away forpurposes of clarity, and illustrating another embodiment of theinvention.

FIGURE 3 is a schematic perspective view of another embodiment of theinvention with the housing cover removed.

With more particular reference to the drawings, FIG- URE 1 illustratesan arrangement wherein two alloy-type transistors are connected inparallel with each other. The transistors are arranged in a housingwhich includes a housing base plate 1 and housing lid or cover 2. Thetwo transistors are specially selected devices or elements which arevery substantially identical to each other insofar as their electricalcharacteristics are concerned.

When two transistors are provided in a common housing there is theadvantage that they are better thermally coupled than transistors whichhave individual housings, that is, those in which each as its ownhousing. The thermal coupling can even be increased if the transistorsare, as shown in FIGURE 1, soldered to a common base plate. In theembodiment of FIGURE 1 the soldering of the transistors is performedusing collector pills 3 soldered to the housing base plate 1. Bothtransistors have a common emitter connection or post 4 to which theemitter pills 5 are connected by means of electrode leads 6. Inaddition, a common base post or connection 7 is provided which contactsthe two semiconductor bodies 8 via the electrode leads 9.

The transistors shown in FIGURE 1 are electrically decoupled by means ofdecoupling resistors 10 connected in the emitter leads 6. In the samemanner, It transistor systems can be provided in a common housinginstead of the above-described two transistors. The optimum designing ordimensioning of the values of the decoupling resistors is determinedempirically.

Tests have shown that above all a minimal value of resistance should bemaintained. In contradistinction to this, it is not as critical if theresistance is made larger. For example, in an arrangement consisting ofseveral five-watt single transistors according to the invention the useof a resistor of 0.1 ohm in the emitter lead of each transistor isrecommended.

With more particular reference to FIGURE 2, an arrangement isillustrated which includes four transistors each transistor allowing apower handling capability of about 25 watts. The n-type siliconsemiconductor bodies 12 of the transistors have a size of about 1 x 1mm. The

emitter and base electrodes 5 and 11, respectively, are comb-shaped.Both electrodes are formed by evaporation of aluminum. Using a n-typesilicon body the base region contacted by the base electrode can beformed by diffusion of boron. For the diffusion of the emitter zonephosphorous may be used.

The transistors of the arrangement of FIGURE 2 are also thermallycoupled because their semiconductor bodies are provided in a commonhousing and are soldered to the well heat conducting common housingplate 1 consisting for example of molybdenum or an iron nickel alloy.Electrical decoupling of these transistors is obtained with the use ofresistors of 0.1 ohm in the emitter leads. The decoupling elements 10'can also have the function of fuses.

The emitter electrodes E are connected in parallel with one another onthe one hand, and the base electrodes B on the other hand have commonbase leads similar to the arrangement of FIGURE 1, and the post orconnection 4 is provided for the emitters and the post or connection 7is provided for the bases. The common housing includes a housing lid orcover 2' and a housing base plate 1, and in this respect is similar toFIGURE 1.

The arrangement of FIGURE 3 is shown schematically and the housing hasbeen omitted for purposes of clarity. Six electrode leads 12 areprovided which can be used to contact the individual elements of asemiconductor arrangement in accordance with the invention. All of theelectrode leads shown in FIGURE 3 extend from a common electrodeterminal 13 and project outwardly therefrom toward the individualsemiconductor elements in a star-shaped manner. For simplicity, only twoelements 14 and 15 are illustrated and these are soldered to a commonbase plate 16.

The strip-like electrode leads 12 are folded to form a double strip anda dielectric material 17 is provided between the layers and this may,for example, be mica. Because of these arrangements, these leads havethe property of the decoupling resistors because if a dielectricmaterial is positioned between the strip-like portions of theseelectrode leads, the electrode leads not only have an ohmic but also acapacitative effect. Such electrode leads can always be used in place ofelectrode leads with ohmic and capacitative resistors connected inparallel.

The contacting of the electrodes of the individual semiconductorelements takes place by using strip-like leads and with the aid ofstrip-ends 18, and these ends are bent at an angle for the purpose ofsoldering them together with the semiconductor electrodes.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim:

1. A power transistor comprising, in combination:

(a) a housing;

(b) a plurality of substantially similar individual transistor elementsdisposed in said housing and each having an emitter, a base and acollector;

(c) a plurality of emitter resistors, one for each said transistorelement, each connected in series with the emitter of its respectivetransistor element for equalizing the power distribution between saidelements; and

(d) first connecting means electrically connecting together thecollectors of all of said transistor elements and constituting thecollector terminal for said power transistor, second connecting meanselectrically connecting together all of the bases of said transistorelements and constituting the base terminal for said power transistor,and third connecting means electrically connecting together the freeends of all of said emitter resistors and constituting the emitterterminal for said power transistor, whereby all of said elements areconnected to operate in parallel.

2. An arrangement as defined in claim 1 wherein said semiconductorelements are identical with one another with respect to their electricalcharacteristics.

3. An arrangement as defined in claim 1 further comprising a pluralityof leads each connected to a respective electrode of one said transistorelement, at least some of said leads being constituted as electricfuses.

4. An arrangement as defined in claim 1 wherein said housing includes acommon base plate on which all of said transistors are mounted forincreasing their thermal coupling.

5. An arrangement as defined in claim 4 wherein said transistors arealloyed transistors the collector of each of which is constituted by acollector alloying pill soldered to said base plate.

6. An arrangement as defined in claim 4 wherein said transistors arediffused base transistors the collector of each of which is constitutedby a collector zone soldered to said base plate.

7. An arrangement as defined in claim 1 wherein each of said resistorscomprises a connecting strip forming a lead of a respective one of saidelements.

8. An arrangement as defined in claim 7 wherein each said strip isfolded to form a two-layer strip, and wherein each said resistor furthercomprises a dielectric body disposed between said layers.

9. A semiconductor device comprising, in combination:

(a) a housing;

(b) a plurality of interconnected semiconductor diode elements disposedin said housings; and

(c) a plurality of resistors connected between said elements, each saidresistor being composed of a connecting strip of resistive materialforming a lead of a respective one of said diodes.

10. A semiconductor device comprising, in combination:

(a) a housing;

(b) a plurality of interconnected transistor elements each having abase, a collector and an emitter; and

(c) a plurality of resistors connected between said elements each saidresistor being composed of a connecting strip of resistive materialforming a lead of a respective one of said transistors.

11. A semiconductor device, comprising, in combination:

(a) a housing;

(b) a plurality of interconnected semiconductor elements disposed insaid housings; and

(c) a plurality of resistors connected between said elements, each saidresistor including a folded two-layer connecting strip forming a lead ofa respective one of said elements, and a dielectric body disposedbetween the two layers of said strip.

12. An arrangement as defined in claim 11 wherein each said body is madeof mica.

13. An arrangement as defined in claim 11 wherein each said strip hasone end bent at an angle and soldered to the associated electrode of itsrespective element.

References Cited UNITED STATES PATENTS 2,663,806 12/1953 Darlington30788 2,751,545 6/1956 Chase 307-88.5 2,816,964 12/1957 Giacoletto307-885 3,226,603 12/1965 Finn et a1 317-10l 3,231,794 1/1966 Diebold317-234 3,264,531 8/1966 Dickson 317234 JOHN W. HUCKERT, PrimaryExaminer.

'R. F. SANDLER, Assistant Examiner.

